disk: part_efi: parse and store partition UUID

Each EFI partition table entry contains a UUID. Extend U-Boot's struct
disk_partition to be able to store this information, and modify
get_partition_info_efi() to fill it in.

The implementation of uuid_string() was derived from the Linux kernel,
tag v3.6-rc4 file lib/vsprintf.c function uuid_string().

Signed-off-by: Stephen Warren <swarren@nvidia.com>

include/part.h

@@ -94,6 +94,9 @@ typedef struct disk_partition {
 	uchar	name[32];	/* partition name			*/
 	uchar	type[32];	/* string type description		*/
 	int	bootable;	/* Active/Bootable flag is set		*/
+#ifdef CONFIG_PARTITION_UUIDS
+	char	uuid[37];	/* filesystem UUID as string, if exists	*/
+#endif
 } disk_partition_t;
 
 /* Misc _get_dev functions */